Google+    |  KNOWLEDGE BASE  |  HOW TO BUY  |   MY PROFILE 

US & Canada 1-800-786-8545 / International 1-360-292-4050
SEARCH:


What is a "Reverse Return" System?

  • Print this page
    Print this page
  • Remove Highlighting
    Remove Highlighting
  • Edit this Article
    Edit this Article
  • Export to PDF
    Export to PDF

Q.  What is a "Reverse Return" System?

A.  A reverse return system is a type of closed loop system in which the return header is connected to the most hydraulically remote load, as shown in Figure 1. Compared to the direct return system in Figure 2 in which the return header is connected to the load closest to the pump, the reverse return system distributes the flows and pressures more evenly across the system, making it more inherently balanced.

Figure 1: Reverse return closed loop system. 

Figure 2: Direct return closed loop system.

The inherent balance of the reverse return system can be shown when modeled in PIPE-FLO and the systems are calculated. Let's first look at the pressure and flow distributions in the direct return system. Figure 3 shows the direct return system with no controls on the loads and the pump sized for 450 gpm (designed for 150 gpm through each identical load).



Figure 3: Direct return system calculated. Pump sized for 450 gpm.

The inlet pressure to each load decreases the farther the load is from the pump discharge, and the outlet pressure of each load decreases the closer the load is to the pump suction. This creates a larger differential pressure at Load 1 and a decreasing differential pressure across each load the farther the branch is from the supply pump. This differential pressure profile causes the flow rate to decrease from 155.9 gpm at Load 1 to 145.9 gpm at Load 3, a 10 gpm (or 6.4%) variation from minimum to maximum flow rate. The pressures and flow rates are summarized in Table 1 below.

Figure 4 shows the calculations for an identical system with the exception of an additional length of piping on the return header to create a reverse return system.

Figure 4: Calculated reverse return system. Pump sized for 450 gpm.

Just as with the direct return system, the inlet pressures to each load decreases the farther the load is from the pump. However, with the return header connected to Load 3, the outlet pressures decrease from Load 1 to Load 3 (opposite of the direct return system). This causes a smaller variation in the differential pressures across each load in the system. The inherent balance of this reverse return system produces a flow rate variation of 4.4 gpm, or just 2.9%.Table 2 summarizes the pressure and flow distribution in the reverse return system.

There are a couple of additional points to note about the calculated results for the two systems. Because the reverse return system requires an additional length of pipe at least the length of the return header, there is additional head loss that must be overcome by the head of the pump. This requires the total head of the pump in the reverse return system to be higher than the direct return system (147.9 ft vs. 129.7 ft in this example). Along with the added capital cost of the extra piping, the increased pump head results in higher operating cost, and may require a larger pump and motor to meet the demands of the system. Also, the increased pump head results in higher discharge pressures, which may affect the selection of pipe material or schedule and the capital costs of the piping.

The benefits of having an inherently balanced system may out-weigh the additional costs that may be incurred. Depending on the need for exact control of flow for each load, it may be possible to design the system without costly flow control valves and eliminate the associated controllers, wiring, pneumatic tubing, and other support instrumentation. An in-depth cost analysis should be done to determine the best solution for any given application.

Related Articles

No related articles were found.

Attachments

No attachments were found.

Article Details

Last Updated
27th of December, 2010

Version
2007, 2009

Article Type
FAQ

Operating System(s)
Windows XP

Would you like to...

Print this page Print this page Email this page Email this page Remove Highlighting Remove Highlighting Edit this Article Export to PDF

User Opinions (25 votes)

100% thumbs up 0% thumbs down

How would you rate this answer?



Thank you for rating this answer.

Visitor Comments

  1. Comment 1 Posted by: Steve Fafnis

    Please send me the pdf of this article. Please provide a link to the pdf so that I can save them. Thanks, Steve Fafnis

  2. Comment 2 Posted by: Anonymous

    another name is first in first out

  3. Comment 3 Posted by: GTH

    I believe that post #2 should read first in - last out.

Post a comment

To post a comment for this article, simply complete the form below. Fields marked with an asterisk are required.

Entering your email address is optional. It will not be displayed on this page, but may be used by our staff to contact you regarding your comment.

For technical support, please do not use this form. Use our Web Support Form or email solutions@eng-software.com, instead.

   Name:
   Email:
* Comment:
* Enter the code below: